The present invention relates to a process for preparing compositions which are useful as intermediates for dispersants used in lubricating oil compositions or as dispersants themselves. In addition, some of the compositions prepared by the present process are useful in the preparation of high molecular weight dispersants which have superior dispersant properties for dispersing sludge and varnish. Such high molecular weight dispersants also advantageously impart fluidity modifying properties to lubricating oil compositions which are sufficient to allow elimination of some proportion of viscosity index improver from multigrade lubricating oil compositions which contain these dispersants.
It is known in the art that alkenyl-substituted succinic anhydrides have been used as dispersants. Such alkenyl-substituted succinic anhydrides have been prepared by two different processes, a thermal process (see, e.g., U.S. Pat. No. 3,361,673) and a chlorination process (see e.g., U.S. Pat. No. 3,172,892). The polyisobutenyl succinic anhydride ("PIBSA") produced by the thermal process has been characterized as a monomer containing a double bond in the product. Although the exact structure of chlorination PIBSA has not been definitively determined, the chlorination process PIBSA materials have been characterized as monomers containing either a double bond, a ring other than succinic anhydride ring and/or chlorine in the product. [(See J. Weill and B. Sillion, "Reaction of Chlorinated Polyisobutene with Maleic Anhydride: Mechanism Catalysis by Dichloramaleic Anhydride", Revue de l'Institut Francais du Petrole, Vol. 40, No. 1, pp. 77-89 (January-February, 1985).]Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666; 3,381,022) as well as adducts having polyalkenyl-derived substituents adducted with at least 1.3 succinic groups per polyalkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
Commonly assigned International Patent Application No. PCT/US89/04270, Publication No. WO 90/03359, dated Apr. 5, 1990 and entitled "Novel Polymeric Dispersants Having Alternating Polyalkylene and Succinic Groups" discloses copolymers prepared by reacting an unsaturated acidic reactant, such as maleic anhydride, with a high molecular weight olefin, such as polyisobutene, in the presence of a free radical initiator, wherein at least about 20 percent of the total high molecular weight olefin comprises an alkylvinylidene isomer and wherein the high molecular weight olefin has a sufficient number of carbon atoms such that the resulting copolymer is soluble in lubricating oil.
U.S. Pat. No. 4,234,435 to Meinhardt et al., assigned to The Lubrizol Corporation, discloses substituted succinic acylating agents derived from polyalkenes, such as polybutene, and a dibasic carboxylic reactant, such as maleic acid or anhydride, wherein the polyalkenes have a number average molecular weight of about 1300 to 5000 and a ratio of weight average to number average molecular weight of about 1.5 to 4. These acylating agents are further characterized by the presence of an average of at least 1.3 succinic groups for each equivalent weight of substituent group. Meinhardt et al. teach that such acylating agents are prepared by heating the polyalkene and carboxylic reactant with chlorine in a one-step process or, alternatively, by first reacting the polyalkene with chlorine and then reacting the resulting chlorinated polyalkene with the carboxylic reactant. This patent further teaches that such substituted succinic acylating agents and their derivatives are useful lubricating oil dispersant additives which also exhibit viscosity index improving properties.
U.S. Pat. No. 4,873,004 to Beverwijk et al., assigned to Shell Oil Company, discloses an alkyl or alkenyl-substituted succinic anhydride, wherein the alkyl or alkenyl group on the anhydride has a number average molecular weight of from 600 to 1300 and wherein the average number of succinic groups per alkyl or alkenyl group is between 1.4 and 4.0. Beverwijk et al. teach that these alkyl or alkenyl-substituted succinic anhydrides can be prepared by mixing a polyolefin with maleic anhydride and passing chlorine through the mixture, or by reacting a chlorinated polyolefin with maleic anhydride. Beverwijk et. al. further teach that the succinimide derivatives of such substituted succinic anhydrides are useful dispersant additives for lubricating oils.
U.S. Pat. No. 3,367,864 to Elliot et al., assigned to Castrol Limited, discloses in Example I thereof the preparation of a polyisobutenyl succinic anhydride by the reaction of about a 1:1 molar ratio of polyisobutylene and maleic anhydride in refluxing toluene and in the presence of a di-tertiary-butyl peroxide free radical initiator. Elliot et al. further teach that the succinic anhydride product produced by this method is similar to the product obtained by thermally reacting polyisobutylene and maleic anhydride at 240.degree. C. for 30 hours.
It has generally been recognized in the art that the polyisobutenyl succinic anhydride prepared by employing a conventional thermal process is primarily a monomeric one-to-one adduct, that is, having about one succinic group per polyisobutenyl group in the product. However, recent analysis of a number of polyisobutenyl succinic anhydride products produced by following the free radical-initiated process of Example I of U.S. Pat. No. 3,367,864 has resulted in a finding that such products are monomeric adducts containing an average of about 1.6 or greater succinic groups per polyisobutenyl group.
Moreover, European Patent Application Publication No. 0,355,895 A2, published Feb. 28, 1990, discloses a process for the preparation of polyolefin-substituted succinic anhydrides in which the average molar ratio of succinic groups to polyolefin chains is greater than 1.3 to 1, which comprises heating a polyolefin with at least a molar excess of maleic anhydride, wherein the polyolefin employed contains at least 70 percent of the terminal groupings in a structure having an alpha olefinic bond or structures in equilibrium with such alpha olefinic structures. Thus, this European patent application teaches that greater than 1.3 succinic groups per polyolefin group can be obtained when the polyolefin employed is one wherein the predominant isomer is an alkylvinylidene.